The present invention relates generally to printers, and more particularly to a method for operating a media feed motor of a printer.
Printers include those printers which print on a paper sheet (or other type or form of media). Such printers have a paper feed mechanism to move the paper a predetermined distance such as a distance for the printer to print the next line of print. Such mechanisms include a paper feed motor. Conventional methods for operating a media feed motor of a printer to perform a media feed move of a predetermined distance include those which choose a media-feed-motor drive signal which includes a position error contribution substantially equal to the product of a scale factor and the difference between a desired final media position at the end of a media feed move and the actual media position. Other contributions to the media-feed-motor drive signal involve other control parameters and are known to the artisan. The scale factor and the other control parameters are different for different ranges of move distances. For example, the scale factor and the other control parameters for a media feed move between one and two units is different than the scale factor and the other control parameters for a media feed move between two and three units. In some control methods, the media-feed-motor drive signal includes a desired velocity error contribution of the difference between a desired media velocity and the actual media velocity. The chart of the desired media velocity versus actual media position has an acceleration portion, a steady-state portion, and a deceleration portion.
Sometimes, as is known to those skilled in the art, it is desirable to use the control parameters of a particular range of move distances for a media feed move which is greater than the maximum distance of that particular range. However, when a long media feed move needs to be made at a slower velocity than is typical for the long media feed move, using a velocity limit and the control parameters intended for a shorter move results in large velocity overshoot and poor accuracy in the move results. There is also a chance that the system will become unstable. What is needed is an improved method for operating a media feed motor of a printer.
A method of the invention is for operating a media feed motor of a printer to perform a media feed move of a predetermined distance and includes steps a) through c). Step a) includes choosing a position-error scale factor for a media feed move that is within a range of distances. Step b) includes calculating a media-feed-motor drive signal which includes a position error contribution substantially equal to the product of the position-error scale factor and the difference between a desired final media position at the end of a media feed move and the actual media position. Step c) includes modifying the position error contribution in step b) to reduce its effect when the predetermined distance is greater than the maximum distance within the range but not when the predetermined distance is less than the maximum distance within the range.
Several benefits and advantages are derived from the method of the invention. Applicants discovered that reducing the effect of the position error contribution of the media-feed-motor drive signal, when a longer media feed move was performed using control parameters for a shorter move, reduces velocity overshoot, improves accuracy in the move, and reduces the chance that the system would become unstable.